The present invention relates in general to handling semiconductor wafers and, more particularly, to an improved method of handling semiconductor wafers during processing, testing, storing and transporting wherein a wafer is attached to a wafer interposer to form a wafer-interposer assembly that reduces the risk of damage to the wafer and the associated integrated circuit chips.
Modern electronic devices utilize integrated circuits, commonly referred to as xe2x80x9cchips,xe2x80x9d which incorporate numerous electronic elements. These chips are typically manufactured in a wafer format, in which numerous similar devices, known as xe2x80x9cdiexe2x80x9d are constructed on a base made from a silicon ingot. In the past, small diameter wafers were common. Today, however, larger diameter wafers, including wafers having an eight-inch diameter (200 mm) and wafers having a twelve-inch diameter (300 mm) are typical. In addition to the increase in the diameter of the wafers, there has been a dramatic increase in the density of the circuitry on the wafers. As such, modern wafers may contain hundreds if not thousands of die making each wafer highly valuable.
It has been found, however, that the high density circuitry on these larger wafers has an increased susceptibility to stress, vibration and abrasion. In addition, it has been found, that the larger diameter wafers have an increased susceptibility to cracking and breaking. Thus, conventional handling procedures during processing, testing, storage and transportation of wafers have resulted in damage to individual die as well as to entire wafers.
As an example, during wafer level testing using a prober test machine, the wafer must be handled numerous times. These handling steps include loading the wafer onto a tray of the prober test machine using a transfer arm, picking up the wafer with a vacuum pick up device from the tray and placing it into a cassette slot and loading the cassette onto an autoloader which transfers the wafer to a stage using a transfer arm. Once on the stage, the die on the wafer are tested using the prober that must physically contact each die. After testing the transfer arm removes the wafer from the stage and returns it to the cassette. This procedure is repeated for each of the wafers to be tested.
As can be seen, the wafer must be moved numerous times during this testing process by transfer equipment such as transfer arms and vacuum pick up devices. During such movements, the wafer is subjected to numerous potential hazards. For example, if a disruption occurs during a vacuum transfer of a wafer, the wafer may be dropped resulting in cracking or breaking of the wafer. Alternatively, if the wafer is not properly positioned in the cassette, the wafer may fall out. Similarly, if the wafer is not properly aligned within the prober test machine, the prober may damage one or more die. In addition to damaging the wafer, if a wafer is dropped, it can damage processing equipment causing machine down time and maintenance costs. For example, if a wafer breaks, it leaves behind fine silicon particles which must be removed from the processing equipment to avoid causing microscratches on other wafers.
In a like manner, each wafer must be handled numerous times during other steps of wafer processing. In fact, some of the wafer processing steps may occur at different facilities which require placing the wafers in containers and shipping the wafers to another location. In this case, the wafers are typically picked up by a vacuum pick up device and lowered into a container. Again, this process raises the possibility of dropping and breaking the wafer. If the wafer is dropped directly onto another wafer in the container, for example, both wafers may be scratched, cracked or broken.
Therefore, a need has arisen for an improved method for handling wafers during wafer processing, testing, storing and transporting. A need has also arisen for such a method that reduces the likelihood for scratching, cracking, breaking or otherwise damaging a wafer when the wafer must be handled. A need has further arisen for such a method that reduces the likelihood of vibration, abrasion or other stress being placed on the die of the wafer.
The present invention disclosed herein comprises an apparatus and method for improved handling of wafers during wafer processing, testing, storing and transporting. The method and apparatus of the present invention reduce the likelihood for scratching, cracking, breaking or otherwise damaging a wafer when the wafer must be handled. In addition, the method and apparatus of the present invention reduce the likelihood of vibration, abrasion or other stress being placed on the integrated circuit chips of the wafer.
The present invention comprises a wafer-interposer assembly that includes a wafer that is attached to a wafer interposer. The wafer has a plurality of integrated circuit chips each having a plurality of contact pads. These contact pads are electrically connected to a plurality of contact pads on a wafer interposer using, for example, conductive attachment elements. The wafer interposer has a wafer receiving portion and a handling portion. The wafer receiving portion includes the plurality of contact pads that correspond to the contact pads of the integrated circuit chips. The handling portion of the wafer interposer extends outwardly from the wafer receiving portion such that the handling portion is accessible without contacting a wafer in position in the wafer receiving portion. Specifically, the handling portion allows for the manual or automated transfer of the wafer-interposer assembly from one location to another without contact with the wafer. In addition, the wafer-interposer assembly allows for testing of the integrated circuit chips on the wafer without contact with the wafer.
The handling portion of the wafer interposer may take any suitable configuration that improves the handling of the wafer by reducing the likelihood of damaging the wafer. Such configurations may include having a surface area that extends beyond the perimeter of the wafer. Likewise, such configurations may include having a slot, a rail, a hole, a magnet, a set of bearing or the like that interact with transfer or processing equipment to allow secure relocation and position identification of the wafer. Alternatively or additionally, the handling portion of the wafer interposer may include a receiving member attached thereto, such as a handle or an eyelet, to reduce the likelihood of dropping the wafer during movement. The handling portion of the wafer interposer may also include a locking member that interacts, for example, with test equipment to releasably secure the wafer in the proper position. To further protect the wafer and the integrated circuits on the wafer from bending and vibration, the wafer interposer may include one or more stiffeners. Similarly, to protect the wafer and the integrated circuits on the wafer from shock, the wafer interposer may have cushioning members attached thereto. Additionally, to even further protect the wafer and the integrated circuits on the wafer, a cover may be removably attached to the handling portion of the wafer interposer to enclose the wafer thereunder.
In the method of the present invention, the likelihood of damaging a wafer during handling is reduced by electrically connecting the wafer to a wafer interposer that has a wafer receiving portion and a handling portion, thus allowing access to the handling portion of the wafer interposer without contacting the wafer. This method may include accessing a slot, a rail, a hole, a receiving member, a set of bearings or the like of the handling portion of the wafer interposer. The method may also include positioning the wafer by determining the location of a magnet of the handling portion of the wafer interposer. Further, the method may include securing the wafer in a predetermined location by operating a locking member in the handling portion of the wafer interposer. The method may additionally or alternatively include preventing bending, vibrating or shocking the wafer through the use of a stiffener in the handling portion of the wafer interposer, by disposing a cushioning member around at least part of the handling portion of the wafer interposer and by removably attaching a cover to the handling portion of the wafer interposer that extends across the wafer receiving portion.